As the amount of communication traffic increases, the authorized spectrum of a 3GPP becomes insufficient to provide higher network capacity. In order to further improve the utilization rate of frequency spectrum resources, the 3GPP is discussing that how unlicensed spectrums can be used with the help of the authorized spectrum, such as 2.4 GHz and 5 GHz frequency ranges. The unlicensed spectrums are mainly used in systems such as Wi-Fi, BLUETOOTH, radar, medical care uses, and the like.
In general, access technologies, designed for an authorized frequency range, such as Long Term Evolution (LTE), are not applicable to use in unlicensed frequency ranges. Access technologies, such as LTE, have very high requirements for spectrum efficiency and user experience optimization. However, a Carrier Aggregation (CA) function enables the LTE to be deployed in an unlicensed frequency range. The 3GPP provides a concept of LTE Assisted Access (LAA), which can use the unlicensed spectrum with the help of LTE authorized spectrums. The unauthorized frequency spectrum can have two working modes. One working mode is a Supplemental Downlink (SDL), that is, only a downlink transmission subframe is included. The other working mode is a Time Division Duplexing (TDD) mode, that is, both the downlink subframe and an uplink subframe are included. The SDL can only be used by means of CA. However, the TDD mode can be used not only by means of the CA technology, but also by Dual Connectivity (DC), and can also be used independently.
Compared with a Wi-Fi system, the LTE system in the unauthorized frequency range can provide higher spectrum efficiency and larger coverage. Data traffic can be seamlessly switched between the authorized frequency range and the unauthorized frequency range based on the same core network. For users, this means a better broadband experience, a higher speed, a better stability, and more mobility.
Existing access technologies on an unlicensed spectrum, such as Wi-Fi, have a weak anti-interference capability. In order to avoid interference, the Wi-Fi system is designed with many interference avoidance rules, such as Carrier Sense Multiple Access/Collision Detection (CSMA/CD) method. The basic principle of the CSMA/CD method is to monitor whether there are other access points (APs) or terminals on the periphery sending/receiving signaling or data before an AP of Wi-Fi or a terminal sends signaling or data. If there are other APs or terminals on the periphery are sending/receiving signaling or data, monitoring is continued until no sending/receiving of the signaling or data. Otherwise, if there are no other APs or terminals on the periphery which are sending/receiving signaling or data, a random number is generated as a waiting time. In the waiting time, if no signaling or data transmission is detected, the AP or the terminal may begin sending signaling or data after the waiting time is completed. The process is shown as in FIG. 1.
However, due to good orthogonality in the LTE network, the interference level can be guaranteed. Therefore, in the base station and the uplink and downlink transmission of the user, there is no need to consider whether or not there are other base stations or other users around, transmitting data. If the LTE is used in an unlicensed frequency range, there is no need to consider whether or not other devices are used in the unlicensed frequency range. In such a situation, Wi-Fi equipment is subject to great interference. As long as there is a service, the Wi-Fi equipment will transmit data. No monitoring rule exists. The idle state of the channel can be detected only after the transmission of the LTE service is completed. After that, data transmission can be carried out.
Therefore, when the LTE network uses the unlicensed frequency range, one of the key points is to ensure that the LAA can coexist with the existing access technologies (such as Wi-Fi) on a fair-friendly basis. However, there is no Listen Before Talk (LBT) mechanism to avoid collisions in the conventional LTE system.
The LBT mechanism, which is similar to the Wi-Fi, can execute detection based on wideband. That is to say, the LBT mechanism determines whether a whole frequency band is available or not by directly detecting a channel state in the whole large frequency band. The defect is that the spectrum utilization not flexible, causing the frequency spectrum utilization rate to be low. Particularly, if the LAA system of an operator A detects that the LBT channel is idle, the unlicensed frequency range is occupied. In fact, the LAA cell may only be occupying part of Resource Block (RB), another RB is not occupied, and yet another RB is in an idle state. When the LAA system of an operator B detects the LBT channel state, the LAA system of the operator B may detect that the channel is busy, due to the fact that the LAA system of operator A is using part of the resources. Thus data cannot be transmitted. In fact, a part of the RB is not being used at all. In this case, the problem of low frequency spectrum utilization rate arises.
Ensuring that the LTE system is prevented from generating large interference to other systems when the LTE system is working normally in the unlicensed frequency range and improving frequency spectrum utilization rate are problematic.